We have developed sensitive (50 ng of protein) and fast (1-2 days) techniques for identification of proteins incorporating database searching, identification of phosphorylation sites, and identification of ubiquitination sites as well as peptide de novo sequencing based on mass spectrometry. We have applied these techniques in a series of collaborations and made important discoveries, which include (1) identification of the yeast eIF-3 complex (in collaboration with Alan Hinnesbusch in NICHD), (2) the yeast NURF complex (in collaboration with Carl Wu in NCI), (3) identification of in-vivo phosphorylation sites of La protein (in collaboration with Richard Maria in NICHD), (4) identification of the phosphorylation site of MIHCK that is responsible for the activation of the kinase, (5) identification of the phosphorylation site of cbl, (5) identification of ubiquitination sites in CSF receptor and (6) identification of ubiquitination of cbl (all in collaboration with Richard Stanley, Albert Einstein Medical School).